How come red & purple are on opposite, far ends of the electromagnetic spectrum, but when mixing colors together in kindergarten, purple is halfway between red & blue?

Question

Shouldn’t common sense dictate that either both be one, or both be the other?

In: 1934

Answer 1

No, common sense breaks down *really* fast with color. Color is *weird*.

https://en.wikipedia.org/wiki/Spectral_color and https://en.wikipedia.org/wiki/CIE_1931_color_space

https://en.wikipedia.org/wiki/Line_of_purples

https://en.wikipedia.org/wiki/Purple#Relationship_with_violet

Color arises from human visual perception, more biology than physics. The arc with numbers on the CIE diagram linked above represents the colors that are perceived in a pure wavelength. The eye has three types of color receptors that respond roughly to red, green, and blue. Kindergarten/traditional color theory uses red, yellow, and blue as primary colors for paints/pigments. Pigments are subtractive in that a red will absorb the other colors. Mixing the primary paints results in brown or black from absorbing everything. This is roughly how color printing works, but with cyan, magenta, yellow and sometimes black, or CMYK.

Light can also work additively. Shine red, green, and blue lights in the right ratio and you get white. Change those ratios and you can get a bunch of different colors and that’s how TVs and computer displays work, RGB.

Green and blue make cyan, red and green make yellow, blue and red make magenta (roughly), so CMY and RGB are complementary: https://en.wikipedia.org/wiki/Color_mixing Mixing red and green light gives yellow. Mixing red and green paint makes brown.